Thermochromic composition of cobalt ii chloride in cured polyester

ABSTRACT

A thermochromic polymer composition is produced by incorporating a methanol solution of cobalt II chloride in an unsaturated polyester resin and then curing the resin without loss of volatiles.

United States Patent n91 l-leseltine et al.

I45] Mar. 27, 1973 THERMOCHROMIC COMPOSITION OF COBALT II CHLORIDE INCURED POLYESTER Inventors: Robert William Heseltine, Aughton; John BurtDawson, Ormskirk, both of England Assignee: Pilkington Brothers Limited,Liver- $oo1, Lancashire, England Filed: Dec. 16, 1970 Appl. No.: 98,937

Foreign Application Priority Data Dec. 19, 1969 Great Britain..62,069/69 US. Cl. ..252/408, 252/300, 73/356, 260/863, 161/195 Int.Cl. ..G03b 5/22,G01k 11/12 Primary Examiner-George F. Lesmes AssistantExaminer-Roland E. Martin, Jr. Attorney-Sughrue, Rothwell, Mion, Zinn &Macpeak [57] ABSTRACT A thermochromic polymer composition is produced byincorporating a methanol solution of cobalt 11 chloride in anunsaturated polyester resin and then curing the resin without loss ofvolatiles.

9 Claims, No Drawings THERMOCIIROMIC COMIOSITION F COBALT Ill CHLORIDEIN CURED POLYESTER BACKGROUND OF THE INVENTION 1. Field of the InventionThis invention relates to thermochromic polymer compositions havingreversible thermochromic properties; that is the color of the polymerdeepens with increase in temperature, the color change being reversitoble so that it fades when the temperature falls to its original value.

2. Description of the Prior Art It has been known to form athermochromic polymer into a thin film and to protect that film from theatmosphere by some form of hermetic sealing. The known polymercompositions contain water and it has been found essential to maintainthe water content of the polymer in order that the color change cancontinue to take place. In the known polymers the color change isobservable when the temperature of the polymer is raised to about 70 Cfrom room temperature and fades again when the temperature returns toroom temperature.

SUMMARY It has now been discovered that thermochromic polymercompositions can be produced which show a significant color change whenthe temperature of the polymer changes by only a small amount, e.g.,within a range of 40 C, to produce a significant absorption of light butat a much lower temperature than those already mentioned, for example 40C. This discovery employs an unsaturated polyester resin in which up topercent by volume of a solution in an alcohol, preferably methanol, ofcobalt II chloride is incorporated so that solution is trapped in thecured resin thus giving the whole of the polymer the new highlysensitive thermochromic properties.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In carrying out the inventionpolyester resins are used which form clear thermoplastic films, andsuitable resins having this property are those known under the tradename CRYSTIC 191E and CRYSTIC 199, and FILABOND 1346. Slightly opaquethermochromic films are produced using cold curing acrylic resins suchas those known by the trade name ACRULITE.

In one example of our invention, 50 ml of a polyester resin known by thetrade name CRYSTIC 199 and 5 ml of a methanol solution (containing 0.1 MCoCl, and 0.4 M LiCl where M is g. moles/liter) were mixed thoroughly,1.5 gm of a catalyst made by Scott Bader Ltd. and known as CatalystPaste H (a paste dispersion of cyclohexanone peroxide) and 0.2 ml A174Silane" (Union Carbide) were dispersed in the mixture, and then 0.5 mlof an accelerator was added. The accelerator was supplied by Scott BaderLtd. and is a solution of a cobalt soap known as Accelerator E (asolution of cobalt naphthanate).

The surfaces of two glass plates which surfaces were to be the innersurfaces of the laminate were primed with a methanol solution of asilane, e.g., Union Carbide A 174 silane to improve adhesion between theglass and the polymer. The plates were dried and one of the plates, withits primed surface uppermost was edged with a spacer strip of neoprenerubber 1 mm. or

2 mm. thick. The mixture was poured on to the glass plate and the secondplate, with its primed face downwardly facing was lowered into positionon the spacer. The plates were firmly clipped together and maintainedhorizontal for l2 hours at 30 C to cure the resin, after which time theplates were found to be firmly joined together by the polymer filmformed. The glass sandwich formed appeared virtually colorless at 10 Cdeepening in color to blue at 40 C. It was found that such a glasssandwich could be heated repeatedly to C without loss of thethermochromic nature of the polymer interlayer.

It is important when using a polyester resin containing monomericstyrene that when curing is carried out, all or substantially all of themonomeric styrene reacts during the curing to form a cross-linkedstructure as this material can interfere with the thermochromic process.

For example, where monomeric styrene is used, the method of theinvention can be accomplished by forming the polyester resin bydissolving a condensation product of maleic or phthalic anhydride with aglycol in monomeric styrene, adding a solution of cobalt II chloride inmethanol, and then curing by the addition of an organic peroxidecatalyst and an accelerator while keeping the temperature sufficientlylow to avoid evaporation of alcohol during the cure.

The concentration of the compounds dissolved in the non-aqueous solventis chosen according to the degree of absorption required, and thethickness of the film formed, lower concentrations being possible inthicker films. We have varied e.g., cobalt II chloride concentrations inmethanol from about 0.005 to 0.5 M for films having a thickness in therange 1 to 5 mm. Using an alkali metal chloride, e.g., lithium chlorideor potassium chloride, as the source of halide ions, the amount presentcan be varied from 0 to about 0.8 M the greater the concentration ofchloride ion Cl the greater the magnitude of the color change.

Some concentrations of Co" and Cl ions in the solution (in g.ions/liter), which give a good intensity change are set out in thefollowing Table:

TABLE I Concentration Color g. ions/liter Co" Cl' ()"C 60C 0.005 0.5pale pink-blue blue 0.05 0.4 pale pink-blue blue 0.3 0.4 pink-blue blue0.4 0.2 pink-blue blue For example, according to the method of thisinvention, the method can comprise forming a methanol solutioncontaining from 0.2 to 0.5 g. ions per liter of chloride ion Cl and0.005 to 0.4 g. ions per liter of cobalt II ion Co", as described inTable I above, adding 8 percent by volume of that solution to a styrenesolution of an unsaturated polyester resin, and then curing the resin togive a cross-linked structure, without evaporation of the methanolemployed in the solution.

Table II gives a number of further Examples 2 to 1 1 of thermochromicfilms prepared in the manner described above, which films are ofdifferent thicknesses, and contain differing amounts of cobalt IIchloride solution in methanol. All the films formed gave a graduallyincreasing intensity of color, as the temperature rose from 10 to 40 Cand could withstand higher temperatures up to 50 or 60 C without thecolor change being irreversible.

and incorporating up to 10 per cent by volume of that solution in anunsaturated polyester resin, and

TABLE if Example Resin MeOH sol 11:1

2 191E 15 0.5 1.0 2.5 {gzf y ggfi 2 3 100 25 1.0 0.5 2 {8:i Y 4 4 100 251.0 1.0 1.5{g: 8f 3 5 100 75 3.0 2.5 4 1 100 50 2.0 1.0 {g fif fig b 1 711m 25 1.0 0. 5 z. 5 {8 3g} gf b 1. 5 s. 100 15 1.5 1 0 2.5 {5:2 gf 5 0100 15 1.5 1.0 1. 5 5, 8 5

Polymer laminate. b Glass laminate.

The polymer layers produced were found to be completely stable up to 60C. In practice a temperature change of 0 to C produced a most acceptablechange in color and therefore increase in the absorption of white light.

As a further example of the invention for the production of a 2 mm.thick layer of the polymer in a glass laminate good results wereachieved, for example by the incorporation of 8 ml of a methanolsolution containing 0.3 g. ions/liter Co" and 0.4 g. ions/liter Cl, into100 ml of either C199 or C1915 resin and curing with 4 percent catalyst(cyclo-hexanone peroxide) and 2 to 4 percent accelerator (a solution ofcobalt naphthanate). After the resin had been cured the white lighttransmission of the laminate was found to be 68 percent at 0 C anddecreased linearly to 39 percent at 60 C. The color change from a pinkcolor at 0 C to a blue color at 60 C was reversible, the rate of colorchange depending solely on. the rate at which the polymer interlayer isheated or cooled.

Electrical heating means, for example electrical heating wires or anelectrical heating film on one surface of the glass forming part of thelaminate, could be employed for regulating the temperature of thepolymer so that regulation of the current supplied by simple manualadjustment current control device was used to control accurately thecolor and white light transmission of the laminate.

When laminated between two sheets of transparent material glass ortransparent plastics material the thermochromic polymer film isprotected from water vapor.

Alternatively the film may be made water-repellant, or may be coatedwith a material which is impermeable or only very slightly permeable towater.

Such polymer films, whether laminated or not can be employed forimproving the environment by reducing sunlight glare in buildings orvehicles. Sunlight falling 60 on the film heats it to produce athermochromic change in the film to increase white light absorbtion. Byusing electrical heating means as herein described environmental controlis available to the occupant ofa building or a vehicle.

We claim:

1. A method of forming a thermochromic polymer composition comprisingforming a solution in an alcohol of cobalt ll chloride and an alkalimetal chloride,

thereafter curing the resin to give a cross-linked polymer.

2. A method according to claim 1, wherein the alcohol is methanol.

3. A method according to claim 1, wherein the alkali metal chloride islithium chloride.

method according to claim 1, wherein the polyester resin is dissolved inmonomeric styrene and gives a cross-linked structure when cured, withoutloss of volatiles.

5. A method according to claim 4, comprising forming the polyester resinby dissolving a condensation product of maleic or phthalic anhydridewith a glycol in monomeric styrene, adding a solution of cobalt llchloride and an alkali metal chloride, and then curing by the additionof an organic peroxide catalyst and an accelerator while keeping thetemperature sufficiently low to avoid evaporation of methanol during thecure.

6. A method according to claim 1, comprising forming a methanol solutioncontaining 0.2 to 0.5 g. ions/liter of chloride ion Cl and 0.005 to 0.4g. ions/liter of cobalt [1 ion Co", adding 8 percent by volume of thatsolution to a styrene solution of an unsaturated polyester resin, andthen curing the resin to give a cross-linked structure, withoutevaporation of methanol.

7. A thermochromic polymer composition comprising a polyester resinmatrix formed by curing a mixture of an unsaturated polyester resin,said mixture having incorporated therein up to 10 per cent by volume ofa solution in an alcohol of cobalt ll chloride and an alkali metalchloride.

8. A composition according to claim 7, in which the alcohol is methanoland the alkali metal chloride is lithium chloride.

9. A composition according to claim 8, in the form of a sheet 2 mmthick, wherein said resin matrix has been cured with 4 percent by volumeof a catalyst and 2 to 4 percent by volume of an accelerator, and 8percent by volume of a methanol solution containing 0.3 g. ions/liter ofcobalt II ion Co" and 0.4 g. ions/liter of chloride ion Cl has beenincorporated in the resin prior to curing, the white light transmissionof which sheet is 68 percent at 0 C and decreases linearly to 39 percentat C.

2. A method according to claim 1, wherein the alcohol is methanol.
 3. Amethod according to claim 1, wherein the alkali metal chloride islithium chloride.
 4. A method according to claim 1, wherein thepolyester resin is dissolved in monomeric styrene and gives across-linked structure when cured, without loss of volatiles.
 5. Amethod according to claim 4, comprising forming the polyester resin bydissolving a condensation product of maleic or phthalic anhydride with aglycol in monomeric styrene, adding a solution of cobalt II chloride andan alkali metal chloride, and then curing by the addition of an organicperoxide catalyst and an accelerator while keeping the temperaturesufficiently low to avoid evaporation of methanol during the cure.
 6. Amethod according to claim 1, comprising forming a methanol solutioncontaining 0.2 to 0.5 g. ions/liter of chloride ion Cl and 0.005 to 0.4g. ions/liter of cobalt II ion CoII, adding 8 percent by volume of thatsolution to a styrene solution of an unsaturated polyester resin, andthen curing the resin to give a cross-linked structure, withoutevaporation of methanol.
 7. A thermochromic polymer compositioncomprising a polyester resin matrix formed by curing a mixture of anunsaturated polyester resin, said mixture having incorporated therein upto 10 per cent by volume of a solution in an alcohol of cobalt IIchloride and an alkali metal chloride.
 8. A composition according toclaim 7, in which the alcohol is methanol and the alkali metal chlorideis lithium chloride.
 9. A compositIon according to claim 8, in the formof a sheet 2 mm thick, wherein said resin matrix has been cured with 4percent by volume of a catalyst and 2 to 4 percent by volume of anaccelerator, and 8 percent by volume of a methanol solution containing0.3 g. ions/liter of cobalt II ion CoII and 0.4 g. ions/liter ofchloride ion Cl has been incorporated in the resin prior to curing, thewhite light transmission of which sheet is 68 percent at 0* C anddecreases linearly to 39 percent at 60* C.